The invention relates to a high-pressure sodium discharge lamp comprising a discharge vessel enclosed with intervening space by an outer bulb and having a ceramic wall, in which two electrodes are present with respective tips spaced apart by a distance D and in which at least over the distance D the discharge vessel has a substantially circular cross-section with an internal diameter d.sub.i, the lamp radiating light with a colour temperature T.sub.c of at least 2400K under nominal operating conditions.
A lamp of the type described in the opening paragraph is known from GB-A-2,083,281. The known lamp radiates white light with a good colour rendering expressed as the colour rendering index R.sub.a with a value of more than 80. Generally, the region in the colour triangle bounded by straight lines through points having coordinates (x; y); (0.400; 0.430), (0.510; 0.430), (0.485; 0.390) and (0.400); 0.360) can be regarded as representing "white" light in the case of light radiated by high-pressure sodium lamps. The colour temperature T.sub.c lies between approximately 2300K and 4000K in this case.
The known lamp can be used to replace an incandescent lamp, for example in accent lighting applications. The colour temperature T.sub.c of the known lamp, however, is relatively low for this in comparison with the light radiated by incandescent lamps. A colour rendering index R.sub.a above 80 is necessary for incandescent lamp replacement. The maximum achievable colour rendering index value for practical high-pressure sodium lamps is between 80 and approximately 85.